Method for solvent extraction of oil



June 21v, 1,938.

D. R.l MERRILL ,-3 Treazzg Siage 14 l 125 J, 'fr ,l5 l 4 -Treczmg 'zge@Liked-NAH, A,"f 2,' 20 Treazzzng Siege T 7) (Cooler 42 '17 I0 "511 (19-fa l Sepczzczorf" 6 l IN VEN TOR.

TORNEY.

Patented June 21V, 1938 UNITED sTATts- 2,121,325 METHOD FORSLVENTEXTRACTION V01"" OIL David R. Merrill, Long Beach, Calif.,assignor to Union Oil Company of California, Los Angeles, Calif., acorporation of California Application April 281, 1936, Serial No. 76,7762 claims. (cries-eis) This invention relates to a process for theseparation of oil into fractions by means of solvents and is acontinuation in part of my .copending application Serial No. 686,941filed 5 August 26, 1933 and my application Serial No.

51597 filed January 14, 1935.

Most crude oils are complex mixtures of hydrocarbons and contain Varyingproportions of paraiinic, naphthene, aromatic and unsaturated l0hydrocarbons. In the production of lubricating oil for internalcombustion motors it is desirable to produce a finished oil thatexhibits a low temperature viscosity susceptibility, i. e., one whichshows a minimum change in viscosity for a given change in temperature.Theparaiiinic hydrocarbons are characterized by a relatively ,lowtemperature Viscosity susceptibility, whereas aromatic and highlyunsaturated hydrocarbons are characterized by a relatively hightemperature viscosity susceptibility. The term viscosity gravityconstant is a means of expressing the' temperature viscositysusceptibility of an oil.

This constant is described in a Journal of In-` dustrial &` EngineeringChemistry, volume 20, page 41, of 1928, by Hill and Coates. A high valuerepresents a high degree of non-paraffinicity or a high temperatureviscosity susceptibility, while low values indicate vrelatively greaterparainicity or a lower temperature visi cosity susceptibility.Lubricating oils from nat- Iural crudes range from .903 for extreme GulfCoast type to .807 for an extreme Pennsylvania type.

For purposes of identification in this applica-` 354 tion, oil fractionswhich exhibit a low viscosity gravity constant will be referred to asparaiinic oil fractions and oil fractions which possess a high viscositygravity constant will be referred to as non-paraiiinic oil fractions.4:0` In the conventional method of employing solvents to separateparaffinic and non-paraffinic hydrocarbons of petroleum oils a solventis chosen which exercises a preferential solvent action for thenon-paraflinic hydrocarbons present 45' in the oil. These solventsinclude aniline, nitrobenzene, furfural, beta beta dichlorethyl ether,phenol, cresylic acid, chloraniline, chlorphenol, sulfur dioxide, orsulfur dioxide modified with benzene. lSuch preferential solvents aremixed 50 with the oil and the mixtures maintained at such temperaturesthat separation into two phases occurs. The phase containing the moreparafnic fractions is known as a ralnate phase and the phase containingthe less parafiin- 55 fic fractions is known as the extract phase.

The separation of the hydrocarbon components by this process is neversharp however, and the extract phase will always contain more or less ofthe parainic fractions and the raffinate phase will correspondinglycontain more or less of the 6 non-paraflinic fractions.

Among other factors` governing the quantity of parafiinlcIv fractionspresent in the extract phase is the composition of the raffinate phasewith which the extract phase is in equilibrium. 10 In the production ofa relatively high paraflinic raflinate phase a relatively highconcentration ofthe parainic hydrocarbons will be found in the extractphase. Thus in the production of a highly paraiiinic raliinate therewill be a rela- 15 tively high loss of paraflnic oil fractions in theextract phase.

In my copending application Serial No. 686,941 filed August 26, 1933, Ihave described this phenomena in detail. scribed a process wherein anoil was extracted with a selective solvent, a high grade raffinate wasremoved from the extraction system and an extract phase containing moreor less valuable paraflinic oil fractions was (a) cooled for the 25removal of valuable parafnic oil fractions which were returned to theextraction system and (b) extracted to recover valuable paraflinic oilfractions from the extract phase which were returned to the feed.

A similar process has also been described in my copending applicationSerial No. 1597 led January 14, 1935. In the latter application extractphase produced by contacting oil with a selective solvent of the cla/ssdescribed above was cooled for the separation of the more paraiiinicfractions present in the extract phase. The more parainic oil fractionsrecovered by cooling the extract phase were then returned to the oilfeed stream and this mixture was then contacted with a selectivesolvent.

In the present application I am employing the principle which Idisclosed in my two prior led applications described above. In thepresent process, a raw oil is contacted with one of the selectivesolvents described above to produce a raffinate phase and an extractphase. The more paraiiinic oil fractions are then recovered from theextract phase and are commingled with the raw oil entering theextraction system in a regulated amount. By returning the parafnic oilfractions recovered from the extract phase continuously and in aregulated amount, I am able to establish equilibrium throughout theentire extraction process.

In that application I de- 2li The inventilon therefore resides inrecovering a second quality railiniate from the extract phase whichcontains valuable paraffinic fractions and returning it to the feedstock. The rate of addition of this second quality raffinate to the feedstock must however be continuous or controlled since otherwise the oilentering the extraction system will be fluctuating in composition andwill not admit the establishment of that steady state which is requisitefor the realization of high efficiency in the extraction. The inventiontherefore resides in maintaining a constant composition of the blend offeed stock and second quality raffinate which is recovered from theextract phase. rI'he invention further resides in blending secondquality raffinate obtained from the feed stock inr controlled amounts sothat the feed stock entering the extraction system is of constantquality and extracting this constant quality oil with a constantquantity of selective solvent under carefully controlled temperatureconditions, that is, a non-fluctuating temperature.

My invention will be understood by referring Ato the accompanyingdrawing. In the figure the raw oil is countercurrently extracted withone of the foregoing selective solvents thereby producing a finalraiiinate and a nal extract, the raffinate comprising the moreparaflinic oil fractions of the feed and the extract comprising therelatively less paraffinic oil fractions of the feed. Referring morespecifically to the drawing, selective solvent is fed into theextraction system through line I. Raw oil is introduced through line 2.A final raffinate is withdrawn through line 8 and a final extract iswithdrawn through line 9. Zones 3, 4 and 5 are employed to permit theseparation of the solvent and the oil into phases. From the uppersection of each of these zones a raffinate phase is withdrawn and fromthe lower section of each of these zones an extract phase is withdrawn.The extract phase withdrawn from zone 5 passes through a cooler 'I wherethe temperature of the solution of oil dissolved in the selectivesolvent is lowered sufficiently to cause the more paraiiinic oilfractions contained in the oil solvent solution to be forced out of thesolution. The cooled mixture from the cooler 1 passes by means of lineI8 into separator 6 where the more paraflinic oil fractions forced outof solution by the lowered temperature from an upper second raffinatephase in zone 6 are removed through line I9. The final extract phase,that is the lower phase in zone 6, is removed through line 9. Thus theprocess shown in the figure consists of an extraction system in whichoil is countercurrently extracted with a selective solvent and in whichthe more paraiiinic oil fractions are recovered from the extract phaseand returned to the oil feed in a regulated amount so that the oilentering the extraction system is of constant quality, therebypermitting equilibrium to be established throughout the countercurrentextraction system.

Considering the figure in more detail, selective solvent is introducedinto the system through line I, the oil to be extracted, that is the oilfeed, is introduced through line 2. Extract phase recovered fromseparating zone 4 through line I6 is commingled with the oil feed andthis mixture passes into separating zone 5 where a raffinate phase andan extract phase are formed. The raiiinate phase in zone 5 iscontinuously drawn off through line I5 where it is commingled with theextract phase withdrawn from separating zone 3 through line I4. Thismixture passs into separating zone 4 where it is permitted to stratifyinto an upper raffinate phase and lower extract phase. The upper rafnatephase is continuously withdrawn through line I3 and mixed with freshsolvent in line I after which this mixture passes into separating zone 3where it is permitted to separate into a final raffinate phase or upperlayer, which is withdrawn through line 8 and a lower extract phase whichis withdrawn through line I4.

The extract phase formed in separating zone 5, that is the lower layer,is continuously withdrawn through lineV I'I and passes through cooler Iwhere the temperature of the soil solvent solution is cooledsufficiently to cause rejection from solution of the more paraflinic oilfractions contained therein. VThe cooled mixture then passes from coolerI by means of layer I8 into separating zone 6 where it is permitted tostratify into a lower layer which is the final extract phase producedand into an upper layer which is a second quality raffinate. The upperlayer of the second quality raffinate is withdrawn from separating zone6 through line I9. The second quality raffinate withdrawn through lineI9 consists of oil fractions which have a different viscosity gravityconstant or viscosity index than the oil feed or stock. In someinstances the Viscosity gravity constant of the fractions recoveredthrough line I9 is lower than that of the oil feed and in some instancesit may be higher than that of the oil feed, depending upon the degree ofcooling of the extract phase in cooler 'I. Since the oil recoveredthrough line I9, that is the second raffinate phase, is of differentquality than the oil feed introduced through line 2, it is veryimportant that the rate at which the oil returning through line I9 tothe feed be maintained constant in order that the oil in line will be ofconstant quality. By maintaining the oil at a constant quality in line20 the equilibrium of the extraction system is never upset. By feedingin a regulated amount of solvent through line I, a regulated amount ofoil through line 2, a regulated amount of second grade raffinate throughline I9 into the feed in line 2, maintaining constant temperatures inzones 3, 4 and 5 and a constant temperature in cooler 'I and zone 6, itis possible to produce a constant quality raffinate through line 8 and aconstant quality extract from line 9.

In some instances more second quality raffinate is produced in separator6 than can conveniently be vreturned to the feed through line I9. Whenthis condition prevails, a portion of the second quality raiiinate iswithdrawn from line I9 through valve II and line I0.

While I have shown in the drawing the recovery of second qualityraffinate from the extract phase by means of cooling, I do not wish tolimit myself to this method of operation since other methods ofrecovering second quality raffinate may also be employed. For example,when phenol is used as a selective solvent, water may be injected intothe extract phase recovered in line I'I, thereby lowering the solventpower of the selective solvent for the more parafflnie fractions andcausing them to be forced out of solution. In other words, addition ofwater to the extract phase consisting of phenol and dissolved fractionsin an equivalent of the cooling means shown in the drawing.

Another method of obtaining the second quality raffinate consists incontacting the extract phase in line II with liquid propane or butaneWhich dissolves the more paraiiinic oil fractions contained therein. Theliquid propane containing the dissolved more paraiiinic fractions of theextract phase is returned to the oil feed in the manner described abovethrough line I9 in a continuous and constant amount so that the oil inline 20 remains of constant quality, that is, the same viscosity gravityconstant. Where propane is used to recover the more paranic oilfractions from the extract phase, it is sometimes desirable to removethe propane from the oil before it is returned through line I9 into theoil feed in line 2. Furthermore, if cresylic acid has been used as theselective solvent, liquid ammonia may be injected into the extract phaseproduced in line I'I, thereby lowering the solvent power of the cresylicacid for the more paraiiinic oil fractions contained in the extractphase. After settlement of this mixture to which liquid ammonia has beenadded in Zone 6 the more parafnic fractions, forced out of solution bythe addition of liquid ammonia, rise to the top of this separating zoneand are withdrawn and returned through line I9 to the feed in line 2.

The following is an example of the method of carrying out my process:100 volumes of raw stock was introduced through line 2. This stock had aviscosity gravity constant of 0.880 and an A. P. I. gravity at F. of19.6. Into line I 0f the extraction system 850 volume percent of amixture consisting of 20% benzene and 80% sulfur dioxide was introduced.Through line 8 of the extraction system 44.0 volumes of rannate wererecovered having a viscosity gravity constant of 0.807. The temperatureof the oil and solvent in zones 3, 4 and 5 including the mixing zones inlines I, I5 and 20 Was 125 F. The temperature of cooler I and separator6 was 55 F. From .the bottom of separator 6 there was withdrawn 56volumes of extract having a viscosity gravity constant of 0.937. Fromthe top of separator 6 there was withdrawn a raflinate phase which wasreturned via line I9 to the feed in line 2 at a rate to maintain thequality of the feed stock entering zone 5 constant (i. e. same viscositygravity constant). Thus in carrying out the process, the temperature ofall of the extraction stages, that is, stages 3, i and 5, are keptconstant, that is, temperature in these stages is not permitted tofluctuate. The temperature in the rejection stage 6 is also kept at aconstant value, thereby producing a rejected oil in line I9 which is ofconstant composition. The rejected oil in line I9'is fed back into theoil feed in line 2 at a constant rate so that blend of oil in line 20 isof constant quality or constant composition and since the amount ofsolvent introduced through line I is constant both in composition and inquantity and since the raw feed introduced through line 2 is constant inquantity, I am able by the process described above to produce a finalrainnate in line 8 of constant'quality and a nal extract in line 9 ofconstant quality.

The invention therefore resides in extracting an oil containing parainicand non-paraflnic oil fractions with a selective solvent capable ofresolving the oil into a raffinate phase comprising the more paraiinicconstituents of the feed stock and an'extract phase comprising the bulkof the selective solvent, the major portion of the nonparaiiinic oidfractions of the feed stock and some of the relatively paraffinic oilfractions which have been dissolved in the extract phase, separating themore parafiinic oil fractions contained in the extract phase either bychanging the composition of the extract phase, cooling the extractphase, or by the addition of modifying agents which cause the moreparaiinic oil fractions contained therein to be forced out of solutionand then returning the more paraffinic oil fractions forced out ofsolution in the extract phase to the feed stock entering the extractionsystem in regulated amounts so that the oil entering the extractionsystems is of constant quality. By maintaining a constant compositionand quantity of feed to the extraction system together with a constantquantity of selective solvent and constant temperatures in theextraction system, it is possible to recover a final rafrinate and afinal extract, each having a constant quality (i. e. constant viscositygravity constant).

The above example is not to be taken as limiting but is merelyillustrative of the invention Which I claim.

1. A process for the separation of oil into fractions which comprisesfeeding oil into an extraction system, countercurrently extracting saidoil with a selective solvent and thereby forming a railinate phase andan extract phase, separating said phases, recovering oil fractions fromsaid extract phase which have a viscosity gravity constant differentfrom the viscosity gravity constant of the feed introduced into saidextraction system, and continuously mixing said oil fractions recoveredfrom said extract phase with the oil feed in a regulated amount so thatthe composition of the oil entering the extraction system will besubstantially of constant quality.

2. In a continuous countercurrent process of separating oil intofractions relatively more paraiiinic and relatively less paraninic incharacter by means of a selective solvent wherein a reflinate phase andan extract phase are produced and oil fractions are recovered from theextract phase having a different viscosity gravity constant from the oilfeed passing to extraction system, the steps of continuously mixing theoil fractions recovered from the extract phase with the Oil feed in aregulated amount whereby an oil mixture.

is produced and later extracted which oil mixture continuously possessessubstantially the same viscosity gravity constant.

DAVID R. MERRILL.

